A sequence of diagrams is made using black and white counters. [Figure - Diagrams 1, 2, 3, 4 with counters] The number of black and white counters in each diagram is shown in the table below. [Table showing Diagram number, Number of white counters, Number of black counters]

1. (a)Complete the table for Diagrams 5 and 6.[1]
2. (b)Write an expression, in terms of n, for the number of white counters in the nth diagram.[1]
3. (c)By considering the number patterns in the table, write an expression, in terms of n, for the number of black counters in the nth diagram.[1]
4. (d)What is the total number of counters in the 20th diagram?[1]

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